Coated abrasive tools generally include an abrasive material, typically in the form of abrasive particles, bonded to a substrate by means of one or more adhesive layers (e.g., make and/or size coat). Polyurethane adhesives have generally been employed for one or more of the adhesive layers in making coated abrasive tools. Typically, a polyurethane adhesive composition, with or without an abrasive material, is applied to a substrate. Depending upon the specific desired application, an abrasive material can be added to the polyurethane adhesive composition to form a slurry which is subsequently applied over the substrate, or alternatively can be applied separately to the polyurethane adhesive coating by gravity or by electrostatic discharge, or in an air stream.
For coating control purposes, the polyurethane adhesives are usually formulated by combining a urethane prepolymer with a curing agent in a suitable solvent. Generally, urethane prepolymers can be classified in two categories, i.e., non-blocked and blocked prepolymers. Blocked urethane prepolymers have reactive functional end groups capped with blocking group(s) to prevent premature reaction that can result in a short pot life. The blocked urethane prepolymers can provide a stable viscosity during the coating process. However, the blocking group(s) has to be removed for the urethane prepolymer to be able to react with a curing agent. Further, special tooling and processes are generally required to remove the blocking group(s) at elevated temperatures. Also, commonly used blocking agents, such as phenol or 2-butanone oxime, are generally hazardous to human beings and the environment. In addition, aromatic amines, such as methylene dianiline (MDA), 4,4′-methylene-dichloro-aniline (MOCA), which are commonly used as the curing agents for the blocked urethane prepolymers, also are generally considered to be hazardous to human beings and the environment. On the other hand, non-blocked urethane prepolymers can react with a curing agent, such as an amine as described above, too quickly, which results in rapid increase of adhesive viscosity and a shortening of the pot life of the adhesive.
Therefore, there is a need to develop new methods of preparing polyurethane adhesives for coated abrasive tools that overcome or minimize one or more of the problems discussed above.